Many technologies are currently being developed to provide the next generation of flat panel, projection, flexible, and micro-displays. Hat-panel emissive displays, which emit light in a lambertian behavior, are considered by consumers to be the most attractive display. Despite the human eye's natural affinity for emissive displays, liquid crystal displays (LCD) currently dominate the commercial display market. Because LCD's utilize light directing films and polarizers, a perceptible variance in image quality is observed with view angle. Furthermore, the vast majority (approximately 90 percent or greater) of light in an LCD never reaches the viewer because of unavoidable absorption in thin film polarizers and color filters, and other optical losses in the LCD. Generally, polarizers transmit only about 40 percent of unpolarized incident light and color filters transmit only about 20 percent to about 30 percent of incident white light.
Cold cathode fluorescent lamp (CCFL) backlights, which provide about 80 lm/W efficiency, generally result in an LCD efficiency of only a few lm/W. Furthermore, the LCD continuously absorbs light at a pixel regardless of whether the pixel is on (i.e., transmissive) or off (i.e., not transmissive). This insensitivity to pixel state leads to very poor panel efficiency for displaying images that utilize only a fraction of the overall number of LCD pixels. Alternative flat panel display technologies, such as inorganic electroluminescent, organic electroluminescent, plasma display panels, and field emission displays, do not require either efficiency-reducing polarizers or heavy color filtering. Regardless, even these alternative display technologies have comparable or lower efficiency to that of an LCD display panel.
The elimination of polarizers and color filters would significantly improve the efficiency of LCD's. Previous attempts to remove the polarizers from an LCD have included using focal conic domains to scatter light from a specular waveguide and replacing the inefficient liquid crystal cell with electromechanical light valves that involve a specular white light guides, diffuse light outcoupling, and heavy color filtering. Such conventional approaches provide only moderate, if any, efficiency improvements over conventional LCD's and suffer from significant inherent drawbacks, such as strong diffuse reflectivity of ambient light and poor contrast between pixel on and pixel off states.
Industrial signage is a segment of the information display marketplace that continues to advance and evolve with the development of a multitude of optical, electrical, mechanical, and chemical technologies. Light emitting diodes (LED's) have increased in performance (lumens/watt) to the point that they are replacing traditional neon and fluorescent tubes in both outdoor and indoor signage. Tiled liquid crystal and projection displays of various technologies, including cathode ray tubes, liquid-crystal light valves, and lasers, are being used to produce large venue displays which can be actively addressed and provide motion/video imaging in a thin, aesthetically pleasing package. While active or passively addressed motion-capable displays are highly desirable and in demand, they are too expensive for the majority of industrial signage applications. Furthermore, LED-based and neon signs cannot produce full-color imaging performance without some form of light modulation. Therefore, most cost-effective LED-based and neon signs are only capable of producing static line-art, albeit reasonably bright static line-art. Additionally, most of these bright static signs employ multiple optical diffusers that require significant air gaps between the light sources and the printed or stylized display material, typically acrylic sheets, or polyester or vinyl sheeting. The need for air gaps results in the need for deep and unwieldy light boxes.
Therefore, a cost efficient signage system capable of producing bright, full color imaging capability with motion-like simulation effects is desirable.